1. Field of the Invention
The present invention generally relates to temperature sensing devices for use in secondary battery packs that include secondary batteries such as lithium ion batteries, and to the secondary battery packs incorporating such temperature sensing devices. More specifically, the present invention relates to an improved temperature sensing device for use in a secondary battery pack, which uses an NTC element (i.e., a negative temperature coefficient thermistor), and to the secondary battery pack incorporating such a temperature sensing device.
2. Description of the Related Art
Conventionally, secondary battery packs have been commonly used as power supplies for use in, for example, mobile communication apparatuses.
FIG. 6 is a block circuit diagram of a conventional secondary battery pack. Referring to FIG. 6, the conventional secondary battery pack includes a secondary battery 24, a hot-side terminal 21 and a reference potential terminal 22 for recharging the secondary battery 24, and a temperature sensing terminal 23 for sensing the temperature of the secondary battery 24. The positive electrode of the secondary battery 24 is electrically connected to the hot-side terminal 21 and the negative electrode of the secondary battery 24 is electrically connected to the reference potential terminal 22. The secondary battery pack also includes FETs 25 and 26, and a controller IC 27 in order to control the operation of the secondary battery 24.
The secondary battery pack further includes an NTC element 28 for sensing the temperature of the secondary battery 24, which is connected between the temperature sensing terminal 23 and the reference potential terminal 22. The NTC element 28 is disposed in proximity to the secondary battery 24 so as to allow for sensing of the temperature of the secondary battery 24. The secondary battery 24 is recharged by a battery charger in accordance with an output from the temperature sensing terminal 23, i.e., in accordance with the temperature of the secondary battery 24.
With the ever decreasing size of electronic apparatuses which incorporate secondary battery packs, such as cellular phones, the secondary battery packs are also becoming smaller in size. Thus, in the secondary battery pack described above, the hot-side terminal 21, the reference potential terminal 22, and the temperature sensing terminal 23 are disposed in proximity to one another. As a result, for example, if the secondary battery pack is put into a clothes pocket when a metallic piece such as a hairpin happens to be in the clothes pocket, the hot-side terminal 21 and the temperature sensing terminal 23 are often short-circuited due to contact with the metallic piece. When such a short-circuit occurs, a terminal voltage of the secondary battery 24 is applied to the NTC element 28. Thus, a short-circuit current flows into the NTC element 28, which sometimes causes burnout of the NTC element 28.
In order to overcome the problems described above, preferred embodiments of the present invention provide a temperature sensing device for use in a secondary battery pack, and the secondary battery pack incorporating the temperature sensing device, in which an NTC element incorporated therein is unsusceptible to short-circuiting and burnout, and reliability is thus greatly improved.
According to a preferred embodiment of the present invention, a temperature sensing device for sensing the temperature of a secondary battery in a secondary battery pack includes an NTC (negative temperature coefficient) element disposed at a predetermined position for sensing the temperature of the secondary battery, one end thereof being electrically connected to a temperature sensing terminal, and a current limiter element connected between the other end of the NTC element and a reference potential.
In the temperature sensing device, the current limiter element is preferably a PTC (positive temperature coefficient) element.
According to another preferred embodiment of the present invention, a secondary battery pack includes a secondary battery, a hot-side terminal and a reference potential terminal for recharging the secondary battery, a temperature sensing terminal for sensing the temperature of the secondary battery, an NTC element arranged to sense the temperature of the secondary battery, one end thereof being electrically connected to the temperature sensing terminal, and a current limiter element connected between the other end of the NTC element and the reference potential terminal.
In the secondary battery pack, the current limiter element is preferably a PTC element.
In the temperature sensing device and the secondary battery pack according to preferred embodiments of the present invention, because the current limiter element is connected between the NTC element and the reference potential, even if the temperature sensing terminal and the hot-side terminal of the secondary battery pack are short-circuited, the current limiter element prevents an overcurrent from continuously flowing into the NTC element, thereby preventing burnout of the NTC element.
Furthermore, when the PTC element is used as the current limiter element, when an application of voltage is stopped after the overcurrent is blocked by the PTC element, the resistance value of the NTC element returns to its initial value, allowing repeated protective operations in case of short circuits.
Other features, elements, characteristics and advantages of the present invention will become apparent from the following detailed description of preferred embodiments with reference to the attached drawings.